1. Field of the Invention
The present invention relates to resin grouts for anchor systems and, particularly, to resin grouts for use in stabilization of reinforcement members, such as rock bolts or cable bolts (referred to herein collectively as either anchor bolts or reinforcement members), used in underground mining operations.
2. Description of Related Art
Currently available resin grout for anchoring reinforcement members in underground mines is typically provided in elongated dual compartment cartridges containing: (1) a curable polyester resin composition; and (2) a catalyst (for example, benzoyl peroxide). The cartridge is generally produced from a thin, rupturable film. After bore holes are drilled for anchor bolts, the cartridges are inserted into the blind end of the bore hole. When an anchor bolt is inserted into the bore hole and rotated, the cartridge ruptures so that the two components are mixed and a curing reaction begins. The gelling or setting time for the curing reaction typically varies from several seconds to many minutes. The anchor bolt is typically spun at a rotational speed of 100 revolutions/minute for between 3 and 10 seconds depending on the resin gel time (typically 20 to 60 revolutions).
As used herein, the terms “grouting,” “grouting systems,” “grout,” and “grout system” mean a substance that hardens to anchor a reinforcing member in a space. For example, grouting can be provided in the form of a cartridge with a compartment housing a polyester resin and a compartment housing a catalyst, such that when the cartridge is shredded and the resin is mixed with the catalyst, a reinforcing member can be anchored in a space. By gel time, it is meant the time that elapses between mixing of the reactive components and the hardening or stiffening of the resin in the mixture, such as is defined in U.S. Pat. No. 4,280,943 to Bivens et al., incorporated herein by reference in its entirety. The gel time of the resin is known as the time for the resin to set up, e.g., typically from 10 seconds to 2 minutes, and, in the United States, typically either 10 seconds, 30 seconds, 60 seconds, or 120 seconds.
Typically, in the United States, resin grouts for mine roof reinforcement members are purchased in a pre-inhibited and/or pre-promoted condition. For example, the base resin typically may have a 20 minute gel time, which may be adjusted through the addition of inhibitors and promoters. In this manner, the polyester resins are purchased with a desired gel time that may be adjusted using inhibitors and promoters to slow down or speed up, respectively, the gel time. The gel time is shorter at higher temperatures and/or with higher promoter content, and vice versa.
The ASTM Designation F 432-04 entitled “Standard Specification for Roof and Rock Bolts and Accessories” provides a Speed Index for chemical grouting materials, which indicates the time from completion of mixing, until an anchorage level of 4000 lb. is achieved when tested according to the laboratory tests of the Standard. According to the Standard, grouting is identified in accordance with the Speed Index classification system in Table I below, where the Maximum Cure Time is to achieve a 4000 lb. test load.
TABLE ISpeed IndexMaximum Cure Time (sec.)1515303060602402406006001000>600
In the United States, polyester resin is typically purchased from a manufacturer in a pre-promoted state. The acquired resin has a specific gel time which, subsequent to purchase, may be adjusted by the purchaser using promoters or inhibitors to speed up or slow down the gel time to meet desired needs. For example, a formulation designated Speed Index 240 would have a Maximum Cure Time of 240 seconds, but the purchaser can add a promoter to the formulation to change the Speed Index to 180, which corresponds to a Maximum Cure Time of 180 seconds. Such Speed Index adjustments (which generally correlates with gel time adjustments) using a promoter thus is done in a batch-wise fashion, requiring an entire batch of resin to be consumed before making an additional gel time change. Additionally, gel time may be dependent on the relative amounts of resin catalyst. As such, if there is higher catalyst content, the gel time is faster and, conversely, if there is less catalyst content, the gel time is slower.
The gel time of a resin grout may vary, e.g., from 10 seconds to 20 minutes. A mine operator typically needs resin grout that will gel in consistent time from one resin cartridge to another and at a time that is acceptable for the particular roof support plan. For example, the roof support plan may involve installing mine roof bolts spaced every four feet, completed within a certain length of time, meaning that the resin grout of each installed bolt must be fully gelled within a defined time period. As such, it may be necessary to control (adjust) the resin grout gel time. To adjust gel time for mine roof support grouting systems, therefore, it is known to inject promoter into the resin. It also is known to separately manufacture two different batches of resins, with each batch having a different gel time and separately pumping each of the two resins into a film cartridge so as to obtain a two-speed grouting system cartridge. In order to differentiate which end represents a particular resin speed, a dye is often included with at least one of the resins but, unfortunately, the resin is somewhat dark in color and, thus, the addition of the dye can be difficult to discern.